The present invention relates to a liquid ejection head for ejecting a solution containing charged particles dispersed therein. More specifically, the invention relates to a liquid ejection head that ejects droplets by making an electrostatic force act on a solution containing charged particles dispersed therein.
Liquid ejection heads for ejecting liquid have been heretofore proposed as exemplified by a thermal type inkjet head which ejects ink droplets by the expansion force of bubbles generated in heated ink, and a piezoelectric type inkjet head which ejects ink droplets by applying a pressure to ink by means of a piezoelectric element.
Recently, another type of inkjet head has been also proposed in which ink containing a charged fine particle component is used and a predetermined voltage is applied to control electrodes of the inkjet head in accordance with image data to control ink ejection based on the electrostatic force to thereby record an image corresponding to the image data on a recording medium.
Various inkjet recording apparatuses are known to be of the electrostatic inkjet recording system (see, for example, JP 10-230608 A, JP 9-277558 A, JP 10-67111 A, JP 11-10911 A and JP 2001-121716 A).
The inkjet head adopting the electrostatic inkjet recording system is advantageous in that the problems having been heretofore pointed out: ink material restricted in the thermal type inkjet head because of partial heating of ink to 300° C. or higher, and complicated and high-cost structure of the piezoelectric type inkjet head can be solved.
The object to be achieved in the inkjet head of the inkjet recording apparatus disclosed in JP 10-230608 A was to consistently eject ink droplets without causing clogging. Each of the ink guides has an ink guide groove (slit) with a predetermined width formed by cutting and its tip portion is pointed, and it is said that the slit contributes to the meniscus stability. However, this apparatus suffers from its insufficient capability to supply ink particles and has a problem associated with continuous ejection in the high-frequency range.
The object to be achieved in the inkjet head recording apparatus disclosed in JP 9-277558 A was to prevent printing unevenness due to pressure head differences among the nozzles not by relying on the formation of ink guides but by forming an approximately hemispherical meniscus in each ink outlet port by means of the pressure of ink coming from the ink supply path and the surface tension of the ink. However, this apparatus has a limitation on the orientation of the nozzle heads and shaking of the nozzle heads may have a detrimental effect on the apparatus.
The object to be achieved in the inkjet head recording apparatus disclosed in JP 10-67111 A was to stabilize the ink concentration by circulating ink in a consistent manner and the apparatus is designed to absorb variations in the pressure difference between the ink chamber and the ink tank. However, this apparatus is not capable of correcting the non-uniformity of pressure among the channels in the head.
As in JP 10-67111 A, the inkjet recording apparatus disclosed in JP 11-10911 A is also capable of correcting the pressure difference between the inlet and outlet of the head by providing the pressure adjusting tube between the ink supply path and the ink recovery path, but the non-uniformity of pressure among the channels cannot be corrected.
The inkjet recording apparatus disclosed in JP 2001-121716 A has the ink pressure sensor disposed in the ink supply path to control the ink supplying pump so that a decrease in ink pressure can be detected before the apparatus is turned to an unprintable state. However, a method of compensating for the pressure variations among the channels in the head is not considered in this apparatus.